ICES advice 2018

nep.fu.11

Norway lobster (Nephrops norvegicus) in Division 6.a, Functional Unit 11 (West of Scotland, North Minch)

Published 31 October 2018


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ICES advice on fishing opportunities


ICES advises that when the MSY approach is applied, and assuming that discard rates and fishery selection patterns do not change from the average of 2015–2017, catches in 2019 should be no more than 3270 tonnes.

To ensure that the stock in Functional Unit 11 is exploited sustainably, management should be implemented at the functional unit level.



Stock development over time

The historical harvest rate has fluctuated around FMSY and has been below FMSY since 2013. The stock has been above MSY Btrigger since 1998.

Figure 1 Summary of the stock assessment of Norway lobster in Division 6.a, Functional Unit 11. Catches (discard data only available from 1990), harvest rate (sum of landings and dead discards in numbers, divided by total abundance), survey abundance (Underwater TV, millions; SSB proxy; approximate 95% confidence intervals). Harvest rates before 2006 may be unreliable due to underreporting of landings. Orange lines represent MSY Btrigger and the FMSY harvest rate proxy.


Summary of the assessment

Assessment summary for Norway lobster in Division 6.a, Functional Unit 11. Recruitment in thousands.


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Year recruitment high_recruitment low_recruitment low_SSB SSB high_SSB catches landings discards low_F F high_F StockPublishNote Purpose Fage fishstock recruitment_age AssessmentYear units stockSizeDescription stockSizeUnits fishingPressureDescription fishingPressureUnits
1981 NA NA NA NA NA NA 2861 2861 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1982 NA NA NA NA NA NA 2799 2799 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1983 NA NA NA NA NA NA 3197 3197 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1984 NA NA NA NA NA NA 4143 4143 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1985 NA NA NA NA NA NA 4060 4060 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1986 NA NA NA NA NA NA 3381 3381 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1987 NA NA NA NA NA NA 4084 4084 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1988 NA NA NA NA NA NA 4035 4035 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1989 NA NA NA NA NA NA 3205 3205 NA NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1990 NA NA NA NA NA NA 2745 2546 199 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1991 NA NA NA NA NA NA 3234 2793 441 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1992 NA NA NA NA NA NA 3912 3559 353 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1993 NA NA NA NA NA NA 3222 3193 29 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1994 NA NA NA 698 820 942 5251 3614 1637 NA 31.5 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1995 NA NA NA NA NA NA 4511 3655 856 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1996 NA NA NA 465 541 617 3195 2872 323 NA 23.5 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1997 NA NA NA NA NA NA 3332 3046 286 NA NA NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1998 NA NA NA 771 898 1025 2508 2441 67 NA 12.2 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
1999 NA NA NA 647 794 941 3530 3257 273 NA 20.7 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2000 NA NA NA 1032 1166 1300 3347 3247 100 NA 12.1 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2001 NA NA NA 959 1092 1225 3419 3259 160 NA 13.0 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2002 NA NA NA 1188 1337 1486 3717 3440 277 NA 11.5 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2003 NA NA NA 1540 1751 1962 3568 3269 299 NA 8.5 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2004 NA NA NA 1576 1751 1926 3284 3082 202 NA 7.8 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2005 NA NA NA 1376 1540 1704 3456 2949 507 NA 9.4 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2006 NA NA NA 1597 1762 1927 4923 4166 757 NA 12.8 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2007 NA NA NA 1056 1206 1356 4192 3978 214 NA 14.7 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2008 NA NA NA 890 1047 1204 3993 3799 194 NA 16.5 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2009 NA NA NA 968 1195 1422 3823 3496 327 NA 13.7 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2010 NA NA NA 1062 1293 1524 2541 2413 128 NA 7.0 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2011 NA NA NA 1500 1726 1952 2851 2697 154 NA 6.3 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2012 NA NA NA 710 891 1072 3755 3542 213 NA 18.7 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2013 NA NA NA 1197 1403 1609 3777 3413 364 NA 10.0 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2014 NA NA NA 1080 1251 1422 3334 3257 77 NA 9.6 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2015 NA NA NA 1075 1445 1815 3145 3002 143 NA 7.9 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2016 NA NA NA 1132 1422 1712 3795 3529 266 NA 10.7 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent
2017 NA NA NA 901 1050 1199 2512 2448 64 NA 9.3 NA Stock published Advice NA nep.fu.11 NA 2018 tonnes UW TV index individuals Harvest rate Percent

* Values prior to 2006 may be underestimates because of underreporting of landings. ** Dead + surviving discards.


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Figure 2 Catch length–frequency distribution and mean size in catches and landings of Norway lobster in Division 6.a, Functional Unit 11. Vertical lines are minimum landing size (20 mm) and 35 mm.


Stock and explotation status


ICES assesses that fishing pressure on the stock is below FMSY, while spawning stock size is above MSY Btrigger.


Table 1 State of the stock and fishery relative to reference points for Norway lobster in Division 6.a, Functional Unit 11.


Catch scenarios


Table 2 The basis for the catch scenarios. Norway lobster in Division 6.a, Functional Unit 11.
Variable Value Notes
Stock abundance (2019) 1215 million UWTV Survey 2018 (number of individuals)
Mean weight in wanted catch 25.83 g Average 1999–2017
Mean weight in unwanted catch 10.97 g Average 1999–2017
Unwanted catch 10.6% Average 2015–2017 (proportion by number)
Discards survival 25% Proportion by number
Dead unwanted catch 8.2% Average 2015–2017 ( proportion by number)


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Table 3 Annual catch advice and scenarios for Norway lobster in Division 6.a, Functional Unit 11; discarding is assumed to continue at the recent average. All weights are in tonnes.

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Basis Total.catch Dead.removals Wanted.catch Dead.unwanted.catch Surviving.unwanted.catch Harvest.rate.. X..advice.change..
ICES advice basis
3 MSY approach 3270 3231 3113 118 39 10.8 16.0
Other scenarios
5 FMSY lower 2542 2512 2421 91 30 8.4 -9.8
6 FMSY upper*** 3270 3231 3113 118 39 10.8 16.0
7 F2017 2815 2781 2680 101 34 9.3 -0.1
* By number. ** Advice value 2019 relative to the advice value 2018. *** FMSY upper = FMSY for this stock.


The change in advice is a result of the inclusion of the 2018 survey and updating mean weights and discard rates.

Catch scenarios plot

The following plot resumes Fishing mortality scenarios (see Table 3) and the related estimates of Catch and next years’ Spawning Stock Biomass. Vertical and horizontal dashed lines show the available reference points (see also Reference Points section). In the hover text appearing in each point is indicated the value in tonnes (of Cath or of SSB) and the scenario represented. At the same time, in the horizontal axis will show up the corresponding F value.

This plot is produced with plotly. Among available features, it can be downloaded as .png and it is possible to zoom in and out.


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Basis of the advice


Table 4 The basis of the advice for Norway lobster in Division 6.a, Functional Unit 11.
Advice basis MSY approach.
Management plan The EU has proposed a multiannual management plan for the Western Waters, which is not yet finalized (EU, 2018).



Quality of the assessment


Since 1994 the underwater TV survey (UWTV) has provided abundance estimates by functional unit (FU) with acceptable precision. The UWTV survey for FU 11 does not cover Nephrops grounds in the inshore waters and sea lochs, waters that are typically fished by smaller vessels. The total area of these grounds is estimated to be less than 5% of the total stock areas and therefore the exclusion of these inshore areas from the survey is not considered to impact the quality of the assessment.

In 2017, observer sampling from the Scottish Industry–Science observer sampling scheme was extended to include sampling of Norway lobster catches in FU 11. As a result the sampling levels have increased and discard proportions are more precisely estimated.

Biological sampling for this stock is considered sufficient.

The long-term average (rather than a three-year average) was considered more appropriate as input for the mean weight in landings and discards in the calculation of catch scenarios. This is due to interannual variation.


Issues relevant for the advice


From 2016, the EU landing obligation was applied to all catches of Norway lobster fisheries in ICES Subarea 6, with several exemptions. Observations from the 2016–2017 fishery indicate that some discarding above the minimum conservation reference size (MCRS) continues and has not changed markedly (Figure 3). Consequently, ICES is providing advice for 2019 assuming average discard rates as observed over the last three years, which is considered to be a more realistic assumption.

For FU 11, the absolute density observed in the UWTV survey is intermediate compared to other Nephrops FUs, with an average density of around 0.6 individuals m−2. This suggests the stock may have a medium productivity capability. Historical harvest ratios in this FU have been around F35%SPR and landings have been relatively stable in the last thirty years. For these reasons, F35%SPR (combined between sexes) is considered to deliver high long-term yield with a low probability of recruitment overfishing and is therefore chosen as a proxy for FMSY.

A single TAC covers the entire ICES Subarea 6. Management should be implemented at the functional unit level to ensure that fishing opportunities are in line with the scale of the resource for each of the stocks and the corresponding MSY approach.


Figure 2 Norway lobster functional units in subareas 6 and 7.



Reference Points


Table 5 Reference points, values, and their technical basis. Norway lobster in Division 6.a, Functional Unit 11.



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Framework Reference.point Value Technical.basis Source
MSY approach MSY Btrigger 540 million individuals Lowest observed abundance estimate from UWTV survey time-series. ICES (2016)
FMSY 10.8% harves ra e FMSY proxy equivalent to F35%SPR combined sexes derived from length-based per recruit analysis. ICES (2016)
Precautionary approach Blim No defined
Bpa No defined
Flim No defined
Fpa No defined
Management plan* MAP MSY Btrigger 540 million individuals MSY Btrigger EU (2018)
MAP Blim No defined
MAP FMSY 10.8% harves ra e FMSY EU (2018)
MAP range Flower 8.4–10.8% harves ra e Consistent with ranges provided by ICES (2016), resulting in no more than 5% reduction in long-term yield compared with MSY. EU (2018)
MAP range Fupper 10.8–10.8% harves ra e FMSY upper value capped at FMSY because it has not been possible to evaluate the probability of SSB < Blim (ICES, 2016). EU (2018)

*Proposed EU multiannual plan (MAP) for the Western Waters (EU, 2018).



Basis of the assessment


Table 6 Basis of the assessment and advice for Norway lobster in Division 6.a, Functional Unit 11.
ICES stock data category 1 (ICES, 2018a).
Assessment type Underwater TV survey.
Input data One survey index (UWTV-FU11); commercial catches (international landings, length frequencies from Scottish catch sampling); fixed maturity parameters from survey data; fixed natural mortalities. Discard survival rate.
Discards and bycatch Included in the assessment since 1990, data series from the majority of the main fleets covering all landings.
Indicators Size structure, mean size, and sex ratio of catches.
Other information The latest benchmark (based on the UWTV survey) was performed in 2013 (ICES, 2013).
Working group Working Group for the Celtic Seas Ecoregion (WGCSE)

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Information from stakeholders

No additional information is available for this stock.


History of the advice, catch, and management

Table 7 . ICES advice, landings and discards of Norway lobster in Division 6.a, Functional Unit 11. All weights are in tonnes.


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Year ICES.advice Landings.advice Catch.advice ICES.landings Total.discards.
1989 3205 NA
1990 2546 199
1991 2793 441
1992 Maintain current effort 3559 353
1993 Maintain current effort 3193 29
1994 Maintain current effort 3614 1637
1995 Maintain current effort 3655 856
1996 Maintain current effort 2872 323
1997 As for 1996 3046 286
1998 Maintain current effort 2441 67
1999 As for 1998 3257 273
2000 Maintain current effort 3247 100
2001 As for 2000 3259 160
2002 Maintain current effort 3440 277
2003 As for 2002 3269 299
2004 Maintain current effort 3082 202
2005 As for 2004 2949 507
2006 No increase in effort 4166 757
2007 No increase in effort and harvest rate of 15% 3200 3978 214
2008 As for 2007 3200 3799 194
2009 No increase in effort and recent average catch < 4100 3496 327
2010 Harvest rate no greater than that equivalent to fishing at F0.1 < 1000 2413 128
2011 MSY transition scheme < 3100 2697 154
2012 MSY approach < 3200 3542 213
2013 MSY approach < 4200 3413 364
2014 MSY approach < 3485 3257 77
2015 MSY approach < 3092 3002 143
2016 MSY approach = 3770** 3529 266
2017 MSY approach = 3814*** 2448 64
2018 MSY approach = 2819*** NA NA
2019 MSY approach = 3270*** NA NA

* Dead + surviving discards. ** Assuming all catches are landed. *** Assuming recent discarding rates.



History of the catch and landings

Table 8 Catch distribution by fleet in 2017 as estimated by ICES for Norway lobster in Division 6.a, Functional Unit 11.
Catch Landings Total.discards
Directed Nephrops fishery | Mixed Nephrops/demersal fishery
99.4% dead | 0.6% surviving 83.4% trawl 14.8% creels | 1.8% trawl 75% dead | 25% surviving
2512 t 2448 t 64 t


Table 9 History of ICES estimates of landings (for Scotland by gear) and total discards of Norway lobster in Division 6.a, Functional Unit 11. All weights are in tonnes.


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Year UK.Scotland UK.Scotland.1 UK.Scotland.2 UK.Scotland.3 UK.Scotland.4 Other.UK…Ireland Total.landings Total.discards.
Year Nephrops trawl Other trawl Creel Below minimum size (BMS) Subtotal Other UK & Ireland Total landings Total discards*
1981 2320 171 370 0 2861 0 2861
1982 2323 105 371 0 2799 0 2799
1983 2784 96 317 0 3197 0 3197
1984 3449 160 534 0 4143 0 4143
1985 3235 117 708 0 4060 0 4060
1986 2641 203 537 0 3381 0 3381
1987 3459 143 482 0 4084 0 4084
1988 3450 148 437 0 4035 0 4035
1989 2603 112 490 0 3205 0 3205
1990 1941 134 471 0 2546 0 2546 199
1991 2229 126 438 0 2793 0 2793 441
1992 2978 149 432 0 3559 0 3559 353
1993 2699 86 408 0 3193 0 3193 29
1994 2916 246 453 0 3614 0 3614 1637
1995 2940 183 532 0 3655 0 3655 856
1996 2354 148 370 0 2872 0 2872 323
1997 2553 102 391 0 3046 0 3046 286
1998 2023 68 350 0 2441 0 2441 67
1999 2792 56 409 0 3257 0 3257 273
2000 2695 28 524 0 3247 0 3247 100
2001 2649 42 568 0 3259 0 3259 160
2002 2775 79 586 0 3440 0 3440 277
2003 2606 45 618 0 3269 0 3269 299
2004 2391 30 661 0 3082 0 3082 202
2005 2270 23 656 0 2949 0 2949 507
2006 3446 23 697 0 4166 0 4166 757
2007 3361 26 591 0 3978 0 3978 214
2008 3229 13 557 0 3799 0 3799 194
2009 2849 34 613 0 3496 0 3496 327
2010 1783 9 621 0 2413 0 2413 128
2011 2109 17 571 0 2697 0 2697 154
2012 2963 12 565 0 3540 2 3542 213
2013 2356 480 575 0 3411 2 3413 364
2014 2752 13 490 0 3255 2 3257 77
2015 2561 23 418 0 3002 0 3002 143
2016 3039 15 475 0.4** 3529 0 3529 266
2017 2041 45 361 na 2447 1 2448 64

* Dead + surviving discards. ** Below minimum size landings are not rounded, showing the reported values. na = Not available



Sources and references

  • EU. 2018. Proposal for a REGULATION OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL establishing a multiannual plan for fish stocks in the Western Waters and adjacent waters, and for fisheries exploiting those stocks, amending Regulation (EU) 2016/1139 establishing a multiannual plan for the Baltic Sea, and repealing Regulations (EC) No 811/2004, (EC) No 2166/2005, (EC) No 388/2006, (EC) 509/2007 and (EC) 1300/2008. COM/2018/0149 final. 30 pp. https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:52018PC0149&from=EN.
  • ICES. 2013. Report of the Benchmark Workshop on Nephrops (WKNEPH), 25 February–1 March 2013, Lysekil, Sweden. ICES CM 2013/ACOM:45. 230 pp.
  • ICES. 2016. EU request to ICES to provide FMSY ranges for selected stocks in ICES subareas 5 to 10. In Report of the ICES Advisory Committee, 2016. ICES Advice 2016, Book 5, Section 5.4.1. 13 pp.
  • ICES. 2018a. Advice basis. In Report of the ICES Advisory Committee, 2018. ICES Advice 2018, Book 1, Section 1.2. https://doi.org/10.17895/ices.pub.4503.
  • ICES. 2018b. Report of the Working Group for the Celtic Seas Ecoregion (WGCSE), 9–18 May 2018, ICES Headquarters, Copenhagen, Denmark. ICES CM 2018/ACOM:13. 1340 pp.